Researchers Solve the Mystery Behind Rice Root Tips Twirling As They Grow

Scientists at Duke University in North Carolina have gained an insight into why the root tips of some rice varieties twirl and wiggle as they grow down into the soil. 

Using a video footage that compressed over 100 hours of rice growth in less than a minute and played back at 15 frames per second, the researchers saw how the rice roots gain their first foothold in the soil. The seed anchors firmly on the ground so that the plants could grow, the roots burrowing down in a winding path.

The researchers were first studying for different lengths of rice roots, how deep they go, and how they change architecture when they made the discovery. Philip Benfey, a professor at Duke’s biology department stated, “This was a classic example of the serendipity of science.”

It was Kevin Lehner, a graduate student, who had pointed out the location of the important gene in making the roots grow longer.

Lehner had studied mutant rice plants and found that their genes that had been mutated were located in the same region of the chromosome and that those plants had longer roots. This led him to set up a video camera to take footage of normal rice plants next to the mutant plant. 

Through the video, researchers found that the normal rice plant had a root tip that twisted in circles. On the other hand, the mutant rice plant had a root that grew straight down.

Benfey explained that the mutant plant doesn’t have a longer root. Instead, it stretches its length straight down while the normal roots grows by the process called circumnutation where it spirals and circles while moving downward. 

He elaborated that this twirling growth is a strategical movement by the sprouting seeds as they need to anchor the plant and rapidly probe down to take in water and nutrients for growth. 

Benfey added, “The primary role is early anchoring. The second role is that the root is going through the primary topsoil and then it gets down to a more compressed area, soil that is compacted naturally or has become hard because of farm equipment. The roots rarely pound their way through that. They must search for pores or small holes.”

The researchers have also learned that the plant hormone auxin is one of the major contributors to the corkscrew growth of a normal plant. Auxin is a substance that promotes stem elongation and it can move around the top of a growing root in a wave-like manner. 

As for plants that don’t have its roots grow in a corkscrew manner, researchers have discovered that a gene called HK1 is what makes the root tips grow straight instead. 

Benfey has noted that both ways of how the plant roots grow are valuable. “There are circumstances where circumnutation is a good thing. That would be if you were trying to plant in soil with lots of obstacles, such as stones or rocks. But there are situations where you don’t want the plant roots to circle but grow straight down fast,” he said. 

In some research, it’s also been shown that other cultivars or rice don’t grow in a twirling manner. 

At Georgia Tech, scientists have turned to use robotics to explore the mechanics of rice root tips. According to a press release, the researchers built a soft pliable robot that unfurls its tip similarly to a root. They set it down on a path with unevenly spaced pegs to study how root behavior works. 

Both research teams at Duke and Georgia Tech plan to do 3D simulations and more robots to understand what really happens with rice plants and their root tips.